Siloxane polymerization in gypsum wallboard

Abstract

A method of making a gypsum board including: preparing an aqueous slurry including a mixture of: calcium sulfate hemihydrate, water at a weight ratio of water to calcium sulfate hemihydrate of 0.2:1 to 1.2:1, and on a dry basis per 100 parts by weight (pbw) calcium sulfate hemihydrate: 0.2 to 2 pbw siloxane, 0.01 to 2 pbw siloxane polymerization catalyst including magnesium oxide and optionally fly ash, and 0.01 to 0.2 pbw triethanolamine (TEOA); allowing the siloxane to polymerize to polysiloxane; and depositing the slurry on a first cover sheet and covering the slurry with a second cover sheet to shape the slurry, and allowing the shaped slurry to set to form the gypsum board. Also, disclosed is the gypsum board resulting from the method.

What is claimed is: 
     
         1 . A method of making a gypsum board comprising:
 preparing an aqueous slurry comprising a mixture of:
 calcium sulfate hemihydrate, 
 water at a weight ratio of water to calcium sulfate hemihydrate of 0.2:1 to 1.2:1, and 
 on a dry basis per 100 parts by weight (pbw) said calcium sulfate hemihydrate:
 0.2 to 2 pbw siloxane, 
 0.01 to 2 pbw siloxane polymerization catalyst comprising magnesium oxide and optionally fly ash, and 
 0.01 to 0.2 pbw triethanolamine (TEOA); 
 
   allowing the siloxane to polymerize to polysiloxane; and   depositing the slurry on a first cover sheet and covering the slurry with a second cover sheet to shape the slurry, and   allowing the shaped slurry to set to form the gypsum board.   
     
     
         2 . The method of  claim 1 ,
 wherein the siloxane polymerization catalyst is mixed with the calcium sulfate hemihydrate,   wherein the siloxane is mixed with a first portion of the water to be used to prepare the aqueous slurry to form a siloxane/water emulsion,   wherein the siloxane/water emulsion is mixed with a second portion of the water used to prepare the aqueous slurry, and   wherein the calcium sulfate hemihydrate/magnesium oxide mixture is mixed with the siloxane emulsion, the triethanolamine and a remainder of the water for the aqueous slurry to prepare the aqueous slurry.   
     
     
         3 . The method of  claim 1 ,
 wherein a first portion of the aqueous slurry is foamed;   optionally a skim layer of a second portion of the aqueous slurry is applied to a first facing;   wherein the foamed first portion of the aqueous slurry is applied as a gypsum core slurry either to the first facing when the skim layer slurry is not present or to the skim layer slurry when present, the gypsum core slurry; and   wherein a second facing is applied to the gypsum core slurry.   
     
     
         4 . The method of  claim 3 , wherein the foamed gypsum core slurry sets to produce a foamed gypsum core having a total void volume of 30 to 90 volume percent. 
     
     
         5 . The method of  claim 1 , wherein the gypsum core slurry has an absence of triethanolamine complexed with a metal. 
     
     
         6 . The method of  claim 1 , wherein the gypsum core slurry has an absence of Portland cement. 
     
     
         7 . The method of  claim 1 , wherein the slurry further comprises one or more additives at 1 to 8 pbw on a dry basis per 100 pbw calcium sulfate hemihydrate, the additives comprising one or more of starches, dispersants, phosphate-containing component, accelerators, retarders, glass fibers, dehydration inhibitors, binders, adhesives, dispersing aids, thickeners, bactericides, fungicides, pH adjusters, colorants, fillers, and mixtures thereof. 
     
     
         8 . The method of  claim 1 , wherein the gypsum core slurry comprises on a dry basis per 100 pbw calcium sulfate hemihydrate:
 0.25 to 1.5 pbw said siloxane,   0.05 to 1 pbw said catalyst,   0.01 to 0.15 pbw said TEOA, and   wherein the weight ratio of water to calcium sulfate hemihydrate is 0.3:1 to 1.1:1.   
     
     
         9 . The method of  claim 1 , wherein the gypsum core slurry comprises on a dry basis per 100 pbw calcium sulfate hemihydrate:
 0.4 to 1.0 pbw said siloxane,   0.15 to 0.4 pbw said catalyst,   0.02 to 0.1 pbw said TEOA, and   wherein the weight ratio of water to calcium sulfate hemihydrate is 0.7:1 to 0.95:1.   
     
     
         10 . The method of  claim 1 , wherein the catalyst comprises the magnesium oxide. 
     
     
         11 . A gypsum board comprising:
 a core layer in the form of a panel, a first cover sheet and a second cover sheet, wherein the core layer is between a first cover sheet and a second cover sheet,   wherein the core layer resulted from setting, between the first cover sheet and the second cover sheet, an aqueous slurry comprising a mixture of:
 calcium sulfate hemihydrate, 
 water at a weight ratio of water to calcium sulfate hemihydrate of 0.2:1 to 1.2:1, and 
 on a dry basis per 100 parts by weight (pbw) said calcium sulfate hemihydrate:
 0.2 to 2 pbw siloxane, 
 0.01 to 2 pbw siloxane polymerization catalyst comprising magnesium oxide and optionally fly ash, and 
 0.01 to 0.2 pbw triethanolamine (TEOA); 
 
   in which the siloxane was allowed to polymerize to polysiloxane.   
     
     
         12 . The gypsum board of  claim 11 , further comprising:
 a first facing and a second facing,   wherein the gypsum core is between the first facing and the second facing.   
     
     
         13 . The gypsum board of  claim 12 , further comprising a skim layer, wherein the structure of the wallboard is layered, in order, the first facing, the skim layer, the gypsum core, and the second facing. 
     
     
         14 . The gypsum board of  claim 11 , wherein the gypsum core slurry has an absence of triethanolamine complexed with a metal. 
     
     
         15 . The gypsum board of  claim 11 , wherein the gypsum core slurry has an absence of Portland cement. 
     
     
         16 . The gypsum board of  claim 11 , wherein the catalyst comprises the fly ash. 
     
     
         17 . The gypsum board of  claim 11 , wherein the first facing and/or the second facing comprises glass fibers, polyamide fibers, polyaramide fibers, polypropylene fibers, polyester fibers, polyvinyl alcohol (PVOH), polyvinyl acetate (PVAc), cellulosic fibers, or combinations thereof. 
     
     
         18 . The gypsum board of  claim 11 , wherein the gypsum core slurry comprises on a dry basis per 100 pbw calcium sulfate hemihydrate:
 0.25 to 1.5 pbw said siloxane,   0.05 to 1 pbw said catalyst,   0.01 to 0.15 pbw said TEOA, and   wherein the weight ratio of water to calcium sulfate hemihydrate is 0.3:1 to 1.1:1.   
     
     
         19 . A gypsum board made by the method of  claim 1 , comprising:
 a core layer in the form of a panel, a first cover sheet and a second cover sheet, wherein the core layer is between a first cover sheet and a second cover sheet,   wherein the core layer resulted from setting, between the first cover sheet and the second cover sheet, the aqueous slurry.   
     
     
         20 . A gypsum board comprising:
 a core layer in the form of a panel, a first cover sheet and a second cover sheet, wherein the core layer is between a first cover sheet and a second cover sheet,   wherein the core layer resulted from setting, between the first cover sheet and the second cover sheet, an aqueous slurry of  claim 1 .